EEG recording studies in humans have revealed the presence of oscillatory rhythms in brain activity, and D oscillations in different frequency bands have been associated with cognitive processes such as working D memory. Additionally, alterations of oscillatory activity are found in psychiatric illnesses such as D schizophrenia. Despite their apparent relevance, however, the role of neural oscillations in cognitive D processes are as yet poorly understood. The proposed project explores these issues using simultaneous D transcranial magnetic stimulation (TMS) and EEG recording. Specifically, the present proposal assesses D two proposals regarding the mechanisms by which TMS influences ongoing neural activity and hence D behavior. The first proposal holds that TMS achieves it effects by injecting electrical noise into task-related D neural areas, producing characteristic declines in performance. However, this proposal is inconsistent with D findings of TMS-related improvements in performance, which have been reported in several studies. Thus, C an alternative account holds that TMS interacts in subtle ways with ongoing neural activity related to the D performance of specific tasks, producing disruptions or improvements in performance depending on the D nature of the interaction. This issue is explored in an experiment comparing the effects of 10-Hz repetitive D (r)TMS on neural activity, to the effects of 10-Hz visual flicker, which is known to produce widespread D entrainment (i.e. disruption) of neural activity to the flicker frequency. Two additional experiments explore 7 task-related changes in neural oscillations, and how TMS can be used to alter such oscillations, producing u improvements or disruptions in performance at the individual subject level. D D The proposed project will help to clarify how neurostimulation methods such as transcranial magnetic D stimulation (TMS) influence ongoing neural activity, and will contribute decisively to our understanding of D the role of neural oscillations in cognitive processes such as working memory. Moreover, the methods D developed here will point the way towards the use of TMS in the exploration and treatment of abnormal D oscillations found in psychiatric illnesses such as schizophrenia.